High-energy Hydrogen II
Teacher Page
Fuel Cells – Futuristic Battery
Student Objectives
The student:
•
will be able to explain the chemical
reaction in the electrolysis procedure
•
will be able to explain the chemical
reaction occurring in the fuel cell
•
will understand how conservation of
energy relates to the electrolysis/fuel
cell procedure
•
will be able to explain the benefits
and disadvantages of using fuel cells
to generate electricity and power
vehicles.
Key Words:
anode
cathode
catalyst
PEM
platinum
Time: 1 hour
Materials
•
PEM reversible fuel cell with gas
storage tanks (1 per group)
•
photovoltaic panel (1 per group) or
transformer, .5 amps or less (1 per
group)
•
wires with alligator clips (2 per
group)
•
small motor and propeller (1 per
group)
•
distilled water
•
stopwatch (or watch with second
hand)
Background
A fuel cell produces electricity. Similar to a battery, a fuel cell converts energy produced
by a chemical reaction directly into usable electric power. But, unlike a battery, a fuel cell does
not get ‘used up’; it can generate electricity as long as it is supplied with hydrogen. Inside a fuel
cell, hydrogen and oxygen combine to produce electricity and water. As a simple
electrochemical device, a fuel cell does not actually ‘burn’ fuel, so it operates pollution-free.
This also makes it quiet, dependable and fuel-efficient.
Inside most fuel cells, a selectively permeable membrane is sandwiched between two
electrodes. Hydrogen gas feeds into the negative chamber (the anode), and oxygen enters the
Florida Solar Energy Center
Fuel Cells - Futuristic Battery / Page 1
other side in the positive chamber (the cathode). As the hydrogen atoms flow through the anode,
a platinum-based catalyst separates the hydrogen protons from their electron. The charged
protons are attracted to the oxygen on the other side and pass through the membrane. The
electrons cannot pass through the membrane, and instead must get to the cathode via an electrical
wire–creating electricity! When the electrons arrive at the cathode they recombine with the
hydrogen protons and the oxygen atoms to make water. This process also generates some heat
which can be used for other purposes.
An individual fuel cell produces low voltage DC electricity. To meet other power needs,
fuel cells are put together in a ‘stack’, to create any voltage needed.
This experiment demonstrates the decomposition of water in a ratio of 2 volumes of
hydrogen gas to 1 volume of oxygen.
2H2O 6 2H2 + O2
In the fuel cell, the reverse of electrolysis takes place; the gases stored during electrolysis
are reconverted into water.
2H2 + O2 6 2H2O
This proves that this electrochemical reaction is reversible.
The first reaction (electrolysis) requires electrical energy, whereas the second reaction
releases electrical energy. In any such energy cycle there will be losses. The conversion of one
form of energy to another is never 100% efficient. The fuel cell, however, is about twice as
efficient as the internal combustion engine.
Procedure
1.
Divide the students into lab groups of 3 - 5 students per group.
2.
Show the class the reverse PEM fuel cell.
3.
Demonstrate how to fill the chambers for the electrolysis procedure:
•
Flip the fuel cell over so the bottom caps are up.
•
Remove the caps.
•
Fill one chamber completely with distilled water. (Remind the students that only
distilled water is used, any other kind of water or any other liquid will ruin the
membrane in the cell.) Make sure you fill the chamber until some water runs
down the center tube.
•
Push the cap on from the center–this pushes out as much ambient air as possible.
•
Repeat with the second chamber.
4.
Demonstrate how to attach the fuel cell to the photovoltaic panel (or transformer):
•
Attach the red wire to the red terminal on the fuel cell and the positive post on the
photovoltaic cell. Repeat with the black wire to the black terminal and the
negative post on the PV cell.
•
If using a transformer, connect the red to red, and the black to black.
•
Tell the students not to reverse the wires (polarity) as this will foul the fuel cell.
5.
Pass out the equipment and have the students complete the experiment in their lab
manuals.
6.
Assist students as necessary.
7.
After the students finish the lab, show them the animation of a fuel cell (listed in Internet
Florida Solar Energy Center
Fuel Cells - Futuristic Battery / Page 2
8.
Sites below).
Discuss the lab or the fuel cell information. Questions you may wish to pose to your
class:
•
Since we know that no energy transformation is 100% efficient, we know that the
electricity produced by the fuel cell is less than the energy needed for the
electrolysis procedure. We also know that energy cannot be created or destroyed,
so what happens to the ‘missing’ energy? (it turns into heat as a by-product of the
reaction)
•
How are fuel cells and batteries alike? (batteries and fuel cells both produce
electricity, they both have anodes and cathodes)
•
How are fuel cells and batteries different? (their chemicals are different, batteries
run out and need recharged while fuel cells will continue as long as they have a
supply of hydrogen)
•
How could we use fuel cells in the future?
•
What are the advantages of using fuel cells to produce electricity? (non-polluting,
no moving parts, quiet)
•
What are the disadvantages of using fuel cells? (no hydrogen infrastructure at the
present time, cost)
Further Research
1.
Research NASA’s use of fuel cells on the space shuttle and the space station.
2.
Providing a reliable supply of hydrogen and an infrastructure for mobile uses such as cars,
poses a host of transportation and storage problems. Have students pick a fuel cell
application (a car, train, home, apartment complex or factory), and work up a plan to
make this application a reality.
3.
Have students create an advertising poster that promotes the use of fuel cells as an energy
source.
Internet Sites
http://www.eere.energy.gov/hydrogenandfuelcells/fuelcells/basics.html
US Department of Energy, Energy Efficiency and Renewable Energy. Fuel Cell
animation
Florida Solar Energy Center
Fuel Cells - Futuristic Battery / Page 3
High-energy Hydrogen II
Florida Sunshine Standards
Benchmarks/Grade Level Expectations
Fuel Cells – Futuristic Battery
.1
Nature of M atter
Energy
How Living Things
Interact W ith Their
Environment
.2
Standard 1
SC.A.1.3-
Standard 2
SC.A.2.3-
X
X
Standard 1
SC.B.1.3-
X
X
Standard 2
SC.B.2.3-
X
Standard 1
SC.G.1.3-
Standard 2
SC.G.2.3-
.3
.4
.5
.6
.7
X
X
X
Benchmark SC.A.1.3.5 - The student knows the difference between a physical change in a
substance and a chemical change.
Grade Level Expectations
The student:
Sixth
•
knows the difference between a physical and chemical change
Seventh
•
knows that chemical changes result in new substances with different characteristics.
Benchmark SC.A.2.3.1 - The student describes and compares the properties of particles and
waves.
Grade Level Expectations
The student:
Sixth
•
understands that particles may be either neutral or have a positive or negative charge
Seventh
•
knows that charged particles will attract or repel each other
Eighth
•
knows that matter is mostly neutral, but that particles can attain a charge by the gain or
loss of electrons.
Benchmark SC.A.2.3.2 - The student knows the general properties of the atom and accepts that
single atoms are not visible.
Grade Level Expectations
Florida Solar Energy Center
Fuel Cells - Futuristic Battery / Page 4
The student:
Sixth
Seventh
•
understands that protons and neutrons are located in the nucleus of the atom while
electrons exist in areas of probability outside of the nucleus
Eighth
•
knows that when electrons are transferred from one substance to another, the general
properties of both substances change.
Benchmark SC.B.1.3.1 - The student identifies forms of energy and explains that they can be
measured and compared.
Grade Level Expectations
The student:
Sixth
•
knows different types of energy and the units used to quantify the energy
•
understands that energy can be converted from one form to another
Eighth
•
knows examples of natural and man-made systems in which energy is transferred from
one form to another.
Benchmark SC.B.1.3.2 - The student knows that energy cannot be created or destroyed, but only
changed from one form to another.
Grade Level Expectations
The student:
Sixth
•
understands that energy can be changed in form
•
uses examples to demonstrate common energy transformations
Eighth
•
understands how the principle of conservation of energy is applied during an energy
transfer.
Benchmark SC.B.1.3.4 - The student knows that energy conversions are never 100% efficient.
Grade Level Expectations
The student:
Seventh
•
knows that useful energy is lost as heat energy in every energy conversion
Eighth
•
knows that energy conversions are never 100% efficient and that some energy is
transformed to heat and is unavailable for further useful work
•
knows that a transfer of thermal energy occurs in chemical reactions.
Benchmark SC.B.2.3.1 - The student knows that most events in the universe involve some form
of energy transfer and that these changes almost always increase the total disorder of the system
and its surroundings, reducing the amount of useful energy.
Grade Level Expectations
Florida Solar Energy Center
Fuel Cells - Futuristic Battery / Page 5
The student:
Sixth
•
understands that energy moves through systems
Eighth
•
understands that as energy is transferred from one system to another there is a reduction
in the amount of useful energy.
•
knows that energy transfer is not efficient.
Benchmark SC.G.2.3.1 - The student knows that some resources are renewable and others are
nonrenewable.
Grade Level Expectations
The student:
Sixth
•
knows renewable and nonrenewable energy sources
Eighth
•
knows that some resources are renewable and others are nonrenewable.
Florida Solar Energy Center
Fuel Cells - Futuristic Battery / Page 6
High-energy Hydrogen II
Key Words/Definitions
Fuel Cells – Futuristic Battery
anode - the negative terminal or chamber, as in a fuel cell
cathode - the positive terminal or chamber, as in a fuel cell
catalyst - a substance that modifies and increases the rate of a reaction without being consumed
in the process.
PEM - Proton Exchange Membrane. Refers to the most common type of fuel cell
platinum - a heavy precious grayish white noncorroding malleable metallic element that fuses
with difficulty and is used especially in chemical ware and apparatus, as a catalyst, and in dental
and jewelry alloys
Florida Solar Energy Center
Fuel Cells - Futuristic Battery / Page 7
High-energy Hydrogen II
Science Journal
Fuel Cells – Futuristic Battery
1,
Fill the water tanks of the fuel cell. Remember:
•
Flip the fuel cell over so the bottom caps are up.
•
Remove the caps.
•
Fill one chamber completely with distilled water. (Use only distilled water, any
other kind of water or any other liquid will ruin the membrane in the cell.) Make
sure you fill the chamber until some water runs down the center tube.
•
Push the cap on from the center–this pushes out as much ambient air as possible.
•
Repeat with the second chamber.
2.
Attach the PV cell (or transformer) using wires with alligator clips:
•
Attach the red wire to the red terminal on the fuel cell and the positive post on the
photovoltaic cell. Repeat with the black wire to the black terminal and the
negative post on the PV cell.
•
If using a transformer, connect the red to red, and the black to black.
•
Remember, do not reverse the wires (polarity) as this will foul the fuel cell.
Begin timing with a stopwatch as soon as you make the second connection. Record the
level of gases at one minute intervals until the hydrogen tank is completely filled and
begins to bubble up. When the hydrogen tank is completely filled, record the time and
disconnect the fuel cell from the PV cell (or transformer).
Time Interval
3.
Hydrogen level
Oxygen level
What did you notice about the ratio of hydrogen and oxygen produced during the
electrolysis procedure?
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Fuel Cells - Futuristic Battery / Page 8
4.
Why did the electrolysis procedure produce this ratio of hydrogen to oxygen?
5.
Attach the fuel cell to a motor and propeller. (This time it doesn’t matter which wire goes
to which terminal on the motor–reversing the wires will only reverse the spin of the
motor.) Begin timing with a stopwatch as soon as you make the second connection, and
record the level of gases at one minute intervals. When the motor stops or the hydrogen
tank is almost empty (only one bubble of hydrogen left), remove the wires and record the
time.
Time Interval
Hydrogen level
Oxygen level
6.
What did you notice about the ratio of hydrogen and oxygen consumed by the fuel cell to
produce electricity?
7.
Why did the fuel cell consume this ratio of hydrogen to oxygen?
Florida Solar Energy Center
Fuel Cells - Futuristic Battery / Page 9
8.
Write a balanced equation for the electrolysis procedure.
9.
Write a balanced equation for the chemical reaction occurring in the fuel cell.
10.
Compare and contrast the electrolysis procedure and the fuel cell procedure.
11.
In the electrolyser, electrical energy is converted into chemical energy. The energy is
stored as hydrogen gas. In the fuel cell, chemical energy is converted into electrical
energy. For a given volume of hydrogen produced and used, will the fuel cell generate as
much electrical energy as was needed to produce the hydrogen in the electrolyser? If not,
why not?
Florida Solar Energy Center
Fuel Cells - Futuristic Battery / Page 10